What is TRT? Testosterone replacement therapy explained

TRT, or testosterone replacement therapy, is a clinically proven treatment for men with confirmed low testosterone. If you're feeling tired, sluggish or like you've lost your edge, low testosterone could be the reason.

TRT works by replacing the testosterone your body is not producing enough of, helping to restore energy, sex drive, mood and muscle mass. Even though TRT is a well-established treatment, many men delay seeking help due to stigma and misinformation, which is why so many men wait years to get help for low T.

Here's how it works, the pros and cons, and how to get started with TRT in the UK.

Key takeaways

• Low testosterone can cause symptoms like tiredness, low sex drive or irritability.
• TRT replaces missing natural testosterone with testosterone medication and can boost sex drive and energy.
• TRT comes in the form of injections, creams, gels or tablets.
• Because testosterone affects almost every system in the body, TRT can bring wider benefits too, including more confidence, improved muscle mass and strength, stronger bones and better blood sugar control.
• An at-home blood test is the first step to finding out whether low testosterone is the cause of your symptoms.

What does TRT mean?

TRT stands for testosterone replacement therapy. It is sometimes also called androgen replacement therapy or testosterone therapy, though TRT is the most commonly used term in the UK. It is a prescription-only treatment available through the NHS or a private clinic and is only appropriate for men with clinically confirmed low testosterone on blood tests, not for men who simply want to boost performance or build muscle.

What does TRT do?

TRT replaces missing natural testosterone with testosterone medication (in the form of injections, creams and gels, or tablets).

TRT might be prescribed when a blood test flags low testosterone levels and you have some of the symptoms of low T to match, such as:

• Low mood
• Low energy
• Brain fog
• Reduced muscle mass
• Low libido or sex drive
• Erectile dysfunction
• Poor sleep

Because testosterone affects almost every system in the body, TRT doesn't just reverse symptoms. It can bring wider benefits too, including:

• More confidence
• Improved muscle mass and strength
• Stronger bones
• Better blood sugar control

How to know if you need TRT?

Most men look into TRT because they feel low in energy, mood, libido or strength. But these symptoms aren’t always due to low testosterone, which is why getting a blood test to check your levels is key before you start TRT.

Low testosterone is surprisingly common. Around 2 to 5% of men overall, and up to 40% of men over 45, have clinically low testosterone. From around 30, levels decline by about 1% per year. Free testosterone, the active form your body can use, falls even faster due to rising SHBG levels.

For an accurate diagnosis, two blood tests at least a week apart are recommended. Your doctor will assess your levels alongside your symptoms before deciding whether TRT is appropriate. Before considering medication, it is worth optimising sleep, diet and alcohol intake, as these heavily influence testosterone levels.

Other causes of low testosterone include:

• Testicular injury or infections (e.g. mumps)
• Brain injury or pituitary problems
• Chronic alcohol or opiate use
• Diabetes
• Genetic conditions (e.g. Klinefelter’s, Kallmann’s)
• Haemochromatosis (iron overload)

How long does TRT take to work?

How long TRT takes to work varies from person to person and depends on the type of treatment you choose. Most men want to know how quickly testosterone injections or other forms of TRT will make a difference, and the honest answer is that it depends.

Short-acting testosterone injections and creams often give the fastest results, while long-acting injections might take a little longer to show the benefits.

Most men notice improvements within the first three months of treatment. At Voy, 90% of men on a TRT plan see symptom relief within 12 weeks. Read TRT before and after stories from Voy patients.

Here’s a typical timeline:

• 1 to 6 weeks: Some men notice improvements in mood, energy and sex drive within weeks.
• 3 to 6 months: By this stage, most men have their treatment plan fine-tuned. Any issues with raised oestrogen, which can get in the way of progress, are usually under control. The main symptoms of low testosterone often improve, and many men notice extra benefits like less body fat, more muscle, and greater strength. Confidence, focus and drive also tend to pick up. TRT can boost red blood cell levels in men with anaemia, improving energy and stamina during exercise.
• 6 months to 1 year: Here’s where many men notice changes to their appearance, such as more muscle mass, less body fat, and sometimes extra body hair. There should be noticeable improvements to low mood and brain fog, too.
• 1 year onwards: Some men take a little longer on TRT to see the full benefits, but at this stage, long-term effects such as stronger bones and sustained physical improvements come into play.

How does TRT make you feel?

The earliest changes are typically emotional rather than physical. Mood, energy and sex drive often improve within the first few weeks, and brain fog tends to lift relatively quickly. Research suggests TRT may improve memory and cognitive function alongside mood in men with confirmed deficiency. Some men experience fatigue or water retention in the early weeks, usually caused by rising oestrogen levels rather than TRT itself. Your clinician can adjust your treatment if this happens.

Pros and cons of TRT

TRT has a strong evidence base and most men with confirmed testosterone deficiency see significant improvements. Here is an honest summary:

Pros:

• Improved sex drive and sexual function, including erectile function
• More energy and reduced fatigue
• Better mood and reduced depressive symptoms
• Increased muscle mass and reduced body fat
• Improved sleep quality with long-term treatment
• Stronger bones

Cons:

• Can affect fertility by suppressing sperm production, though this is manageable with hCG or other fertility-preserving treatments
• Can increase red blood cell count, which is why regular blood monitoring matters
• May accelerate hair loss in men who are genetically predisposed
• Can raise oestrogen levels, causing side effects like water retention, mood changes or breast tissue growth in some men. Aromatase inhibitors can be prescribed to manage this if needed.

For a full breakdown read our guides to TRT benefits and TRT side effects.

How to take TRT?

TRT comes in several forms. The most common is injections, since there are no absorption issues and your clinician can adjust your dose easily.

At Voy, we recommend testosterone cypionate, injected 2 to 3 times per week to keep levels steady. See our guides on how and where to inject testosterone and subcutaneous injections for technique and tips.

If you don't like needles, TRT gels and creams are applied to the skin and absorbed over a few hours.

There is also a tablet form of testosterone, though it is generally less effective than injections. Testosterone pellets and buccal testosterone also exist but are rarely used in UK clinical practice.

There is no single best TRT protocol. The right approach depends on your hormone levels, lifestyle and whether fertility preservation is a priority. Your clinician will personalise your plan based on blood results and adjust it over time. Most men find it takes three to six months before their protocol is fully optimised.

Some men find that microdosing protocols (more frequent, smaller doses) work better for their lifestyle and symptom management.

Is testosterone replacement therapy safe?

The TRAVERSE trial, the largest study of its kind, found that TRT does not increase the risk of heart attacks, strokes, or prostate cancer. You can read more about TRT safety in our full guide.

TRT isn’t totally risk-free, though. TRT increases the number of red blood cells your body produces, which can be great for energy levels, but it can sometimes cause your blood to become too thick, which increases the risk of blood clots. This is why monitoring your health with regular blood tests is important on any TRT plan, so that your doctor can manage TRT side effects if they occur.

TRT can also reduce fertility, so it's important to consider your plans for a future family and discuss these with your specialist doctor, so you take the right medication for your circumstances.

Who should not take TRT?

TRT is not suitable for everyone. Your specialist will screen for the following before recommending any treatment:

• Active or suspected prostate cancer
• Male breast cancer
• Severe or untreated heart failure
• Untreated sleep apnoea. TRT can also worsen pre-existing sleep apnoea, so this is always assessed before treatment begins
• Haematocrit above 50%
• Actively trying to conceive, as TRT suppresses sperm production, though fertility-preserving options exist

What does monitoring on TRT involve?

Starting TRT is the beginning of an ongoing relationship with your specialist. After starting treatment, you will typically have a blood test at around three months to check testosterone levels, haematocrit and PSA. Once your plan is stable, check-ins move to every six to twelve months. At Voy, these follow-up blood tests and consultations are included in your subscription with no hidden costs.

Expert insights from Jeff Foster on TRT safety

"TRT can also reduce your fertility, as it suppresses your natural testosterone production. But if you’re planning on expanding your family and want to start TRT, there are fertility-preserving medicines such as HCG or clomiphene you can take alongside, or instead of, testosterone medication."

Medical Director Jeff Foster - Men’s Health & TRT Specialist

How to get testosterone replacement therapy in the UK

There are two routes to getting TRT in the UK: the NHS or a private clinic. Testosterone is prescription-only and cannot be bought over the counter. Any website offering it without a prescription is operating illegally and the products cannot be guaranteed safe or genuine.

NHS

The NHS provides a low-cost route but access is slow and limited. To be eligible you generally need very low testosterone levels, and the NHS does not usually provide fertility preservation or ways to manage high oestrogen levels.

Private clinics

Private clinics can treat symptomatic men who would be refused on the NHS, with access to a wider range of options including oestrogen management, fertility support and alternatives like clomid. Clinicians at private TRT clinics typically have more specialist experience than a GP.

With both routes to TRT, the main steps to starting treatment are:

1. Initial blood test for testosterone levels
2. Confirmatory blood test for diagnosis
3. Consultation with a clinician
4. Prescription and treatment start
5. Ongoing monitoring and follow-up

How much does testosterone replacement therapy cost?

TRT costs vary by provider, but you can expect to pay from £99 to £250 per month. Be aware that some clinics will not include medications, blood tests, clinic visits, consultations or injection supplies in their charges.

At Voy, subscriptions start at £99/month, covering medication, blood tests, consultations, fertility support, and more.

Getting started with TRT

TRT is safe, effective and can be life-changing for men with low testosterone. Modern research suggests it not only improves quality of life but may even extend it. With the right monitoring and medical support, most men can expect significant, lasting benefits.

Wondering if low testosterone is holding you back? Take our short quiz to see if TRT could help you get back to feeling your best.